There is a strong demand for the development of near-infrared sensitive materials for use in optical information processing and semi-conductor device manufacturing processes.
Such optical information processing includes, for example, high-speed laser-beam printers and optical information storage systems.
To make custom-made semi-conductor devices, near-infrared sensitive photoresists are required for use with computer-aided solid-state diode laser-beam exposure systems.
As the light sources in near-infrared wavelengths, solid-state diode lasers are widely used because of ease of availability. These lasers, including a gallium aluminum arsenide laser, mostly operate in wavelengths from 750 to 870 nm(nanometers). Thus the near-infrared sensitive materials must have high sensitivity in these wavelengths.
Furthermore, for the purpose mentioned above, the materials must be able to be applied to form thin, smooth films of high mechanical strength, high adhesiveness to the given substrate, and high optical quality.
Phthalocyanine compounds are known to be of very low toxicity, thermally and photochemically stable. And their crystals are able to be converted into a near-infrared sensitive form from the near-infrared insensitive form.
Some near-infrared sensitive materials containing phthalocyanine crystal in a near-infrared sensitive form dispersed in a polymer binder are already known.
For example, there is disclosed in Journal of Imaging Science, Vol. 29, No. 4, 1985, page 148, a near-infrared photoreceptor device incorporating chloroindium phthalocyanine wherein the charge photogenerator layer contains chloroindium phthalocyanine dispersed in Vitel PE-200 (Goodyear) polyester resin. The near-infrared sensitivity of the chloroindium phthalocyanine is based on the formation of dimers as building units in the microcrystals. The microcrystals are obtained by ball milling the near-infrared insensitive chloroindium phthalocyanine crystal in the presence of the solvent methylene chloride and the polyester resin.
There is disclosed in U.S. Pat. No. 4,529,688 an ablative infrared sensitive optical recording composition containing as a component thereof a dispersion of a resinous binder and an absorbing infrared sensitive tertiarybutyl substituted vanadyl phthalocyanine obtained by a solvent vapor treatment which causes recrystallization of the phthalocyanine so as to be infrared absorbing. The ablative recording medium, however, requires an air-sandwiched optical disk structure in order to provide a space that can absorb evaporized or sublimed recording material. To fabricate such a complicated disk structure, time-consuming and thus costly processes are required.
Titanylphthalocyanine photoreceptor devices are disclosed in DENSHISHASHIN GAKKAI-SHI, Vol. 25, No. 3, 1986, wherein the infrared sensitive charge generator layer consists of infrared sensitive alphatitanylphthalocyanine microcrystals dispersed in the resinous binder.
Additionally, there is reported in The Chemical Society of Japan, 1986, No. 3, page 393, a magnesium phthalocyanine-polyester dispersed type photoreceptor which is sensitive to laser diode light. The near-infrared sensitive magnesium phthalocyanine of a new morphological structure is prepared by recrystallization from a strong electron donative solvent such as morpholine.
All of the above near-infrared sensitive materials containing phthalocyanine compounds belong to a class of dispersed type compositions. Thus, they have small particles of phthalocyanine crystals dispersed therein, meaning that they are not of high homogeneity or of high optical quality. More particularly stated, they are not highly absorbing at near-infrared wavelengths due to light scattering caused by the small phthalocyanine particles.
A near-infrared sensitive material must be substantially homogeneous and of high optical quality to be truly useful. Therefore, the phthalocyanine compound being used to this aim must be very soluble into a solvent and a binder polymer, and yet be sensitive at near-infrared wavelengths when it is incorporated in the composition, although the phthalocyanine molecule itself is not sensitive at these wavelengths.